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| Titel |
Ammonia fluxes in relation to cutting and fertilization of an intensively managed grassland derived from an inter-comparison of gradient measurements |
| VerfasserIn |
C. Milford, M. R. Theobald, E. Nemitz, K. J. Hargreaves, L. Horvath, J. Raso, U. Dämmgen, A. Neftel, S. K. Jones, A. Hensen, B. Loubet, P. Cellier, M. A. Sutton |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 6, no. 5 ; Nr. 6, no. 5 (2009-05-15), S.819-834 |
| Datensatznummer |
250003745
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| Publikation (Nr.) |
 copernicus.org/bg-6-819-2009.pdf |
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| Zusammenfassung |
Quantification of ammonia (NH3) land-atmosphere exchange is required
for atmospheric modelling and assessment of nitrogen deposition, yet flux
measurement methods remain highly uncertain. To address this issue, a major
inter-comparison of ammonia fluxes over intensively managed grassland was
conducted during the GRAMINAE Integrated Experiment held in Braunschweig,
Germany. In order to provide a robust dataset of ammonia exchange with the
vegetation, four independent continuous flux gradient systems were operated.
Three independently operated continuous wet denuders systems (AMANDA) were
compared with a Wet Effluent Diffusion Denuder (mini-WEDD) system.
Measurements were made at two distances from an adjacent livestock farm,
allowing effects of advection to be quantified in a real landscape setting.
Data treatment included filtering for instrument failure, disturbed wind
sectors and unsuitable micrometeorological conditions, with corrections made
for storage and advection errors.
The inter-comparison demonstrated good agreement in measured ammonia
concentrations and fluxes (relative standard error <20%) for some
periods, although the performance of the ammonia analyzers were variable,
with much poorer agreement on particular days. However, by using four
systems, the inter-comparison was able to provide a robust mean estimate of
continuous ammonia fluxes through the experiment. The observed fluxes were:
a) small bi-directional fluxes prior to cutting (−64 to 42 ng NH3 m−2 s−1),
b) larger diurnally-varying emissions following cutting
(−49 to 703 ng NH3 m−2 s−1) and c) much larger emissions
following fertilizer application (0 to 3820 ng NH3 m−2 s−1).
The results are a salutary reminder of the uncertainty in unreplicated
ammonia flux measurements, while the replication of the present study
provides a uniquely robust dataset for the evaluation of ammonia exchange
processes. It is clear that consistently reliable determination of ammonia
concentrations remains the major measurement challenge. |
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